Draft control means



Nov. 30, 1954 F. w. SUHR DRAFTI QONTROL MEANS 2 Sheets-Sheet 1 Filed April 17, 1951 IN VEN TOR. 1

Nov. 30, 1954 F. w. SUHR 2,695,624

DRAFT CONTROL MEANS Filed April 17 1951 2 Sheets-Sheet. 2

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INVENTOR.

United States Patent DRAFT CONTROL MEANS Frederick W. Suhr, Wisconsin Rapids, Wis., assignor to Preway Inc., Wisconsin Rapids, Wis., a corporation of Wisconsin Application April 17, 1951, Serial No. 221,463

3 Claims. (Cl. 137-113) This invention relates to a draft control means which is applicable to a furnace wherein air, delivered from a blower or the like, is supplied to a burner to support the fuel combustion therein. In the ensuing description a furnace is referred to, but it should be understood that this term includes also many of the various forms of heaters; also, by way of example, an oil burner of the pot type is mentioned, but I would point out that such a burner is only one of many with which the present invention may be advantageously used.

In present day furnaces, it is common practice to support fuel combustion in the burner by the use of an electrically operated blower. In the event of power failure, operation of the blower is stopped and incomplete combustion of the fuel then starts, all due to the lack of air which is necessary for complete combustion. Such a condition is highly unsatisfactory, it might even become dangerous, and remedial steps should be taken as soon as possible.

The draft control means of this invention is designed to operate automatically in the event of power failure with resulting non-operation of a blower that is regularly relied upon to supply air in volume to a burner. The present control utilizes a duplex damper operable by gravity to uncover a large opernng to the atmosphere, thereby permitting a natural draft of air to enter a duct leading to the burner. While the air thus admitted is less than that regularly furnished by the blower, when in operation, it is nevertheless sufiicient to maintain combustion safely and at a reduced level. Whenever the electrical current is restored to the blower, perhaps in a few or many minutes, the damper which is then in open position for admitting atmospheric air, is automatically closed. From that time on, with the blower in operation, air is driven through the duct leading to the burner in a large volume to adequately support the combustion of fuel therein.

It is an object of this invention to provide such a duplex damper which, with failure of the blower, will automatically operate to open up communication with the atmosphere whereby to admit air therefrom to support combustion of the fuel in the burner. It is also an object to accomplish this end by means which is simple and devoid of any unnecessary parts. According to this invention, I provide in the air duct leading to the burner a duplex damper in the form of a sheet metal plate that is pivotally supported at an intermediate point. This plate provides two dampers operating, in alternation, to open and close, respectively, a relatively large opening to the atmosphere and a relatively small opening in communication with the blower. When once installed, such a damper requires no attention, and it may be relied upon to operate automatically whenever the occasion requires and for an indefinite period of time.

It is also an object of this invention to provide, with such a duplex damper, means whereby to maintain a substantially uniform pressure in the air that is delivered to the furnace burner. This is accomplished by a meter ing hole in the damper which coacts with the opening to the atmosphere. Such a regulating device permits some of the air to escape from the duct leading to the burner. whenever the pressure therein exceeds a predetermined amount. This is an important objective because of the many variations which commonly occur in the operational speed of a blower, due to voltage fluctuations, motor condition, etc. Such a pressure regulating means assures that air movingthrough the delivery duct in a volume in excess of that required for the burner will be reduced automatically to a value that is proper and most advantageous for its operation.

A suggestive embodiment of this invention is set forth in the accompanying drawing wherein:

Figure l is a vertical sectional-perspective view of a furnace having a horizontal air supply duct equipped with the present draft control which is installed in the top of the duct;

Fig. 2 is a fragmentary plan view of a motor-blower unit with the draft control of this invention associated therewith;

Fig. 3 is a detail in vertical section, taken on line 33 of Fig. 2, showing the pivotally mounted duplex damper comprised in the draft control;

Fig. 4 is a plan view of the duplex damper per se;

Figs. 5 and 6 are semi-diagrammatic views of an installation thereof upon a vertical wall of the air supply duct, the positions of the duplex damper when the blower is operating and not operating being indicated in Figs. 5 and 6, respectively;

Fig. 7 which is a view similar to Fig. 4 shows a modificat ion in the contour of the dupjlex damper;

Fig. 8 which is a view similar to Fig. 3 shows the duplex damper installed for operation upon a vertical duct wall, as per Figs. 5 and 6; and

Fig. 9 is an elevational view, corresponding to Fig. 2, of the motor-blower unit as it appears when installed on a vertical wall in operative relation to the present duplex damper.

T he conventional furnace F, here illustrated by way of example, encloses a heating drum D upstanding from a chambered base 5 near the floor of the furnace to provide therefor a combustion chamber having means (not shown) for educting tothe atmosphere the products of combustion. Supported within the drum D a suitable distance above the base 5 is a burner B of the pot type formed in its walls with the usual primary and secondary air inlet openings 6 and 7 respectively. In operation a hydrocarbon fuel is supplied to the pot burner at a point near its base from a reservoir through a feed pipe equipped with the usual flow control. These several units are well known at the present time and so need no further illustration or description here.

The drum base 5 is provided with a lateral extension E constituting a horizontal air duct over whose top wall 10 is arranged a motor-blower unit M. The blower of this unit is mounted to rotate upon a horizontal axis within a housing 11 having a lateral inlet opening 12 thereinto. An air discharge duct 14 extends downwardly from the blower housing to join with the top wall 10 of the chambered base extension E at a point where an operating inlet opening 15 is provided therein. In the extension top wall 10 is an auxiliary inlet opening 17 close to the operating inlet opening 15, located upon the side thereof that confronts the drum D. The auxiliary opening, as shown, is of considerably greater area than is the operating opening 15perhaps twice as muchfor a reason that will presently appear.

The two air inlet openings 15 and 17 are desirably formed in a circular mounting plate 20 whereon is an upstanding marginal fiange 21. Upon this plate which is affixed to the extension top wall 10 is secured the motorblower unit base 22 which closely surrounds the discharge duct 14. A single large aperture 23 is provided in the extension top wall, with its margin lying slightly inwardly of the circular mounting plate 20, thereby to assure communication with the interior of the air duct in the drum basielgxtension B through both of the inlet. openings 15 an 1 The auxiliary opening 17 is here shown to be semiovalescent in shape with a long straight side positioned proximate to the operating opening 15; and depending from this straight side is a wall 25 having a pair of spaced cars 26 laterally extended from its lower edge. A duplex damper is provided by a circular plate formed at one side of a diametrical line with a semicircular blower damper 28 and at its opposite side with a semicircular auxiliary damper 29, the one being offset from the other by a transverse connecting wall 30 (see Fig. 4). At the line a where the auxiliary damper 29 joins with the connecting wall 30 there is approximately a right angle, but at the other line b where the connecting wall 30 joins with the blower damper 28 the angle is obtuse. Adjacent the juncture line b is a pair of aligned spacedslots 31 (see Fig; 4) through each of which is extended one of the ears 26' which may be inclined slightly upwardly to provide, in efiect, a pair of hooks whereon the duplex damper plate is pivotally supported withthe dampers at its opposite ends in counterbalaneihgrelation. When operatively assembled in place, the duplex damper plate is free to reel; between twopositions in. one of which (see Fig. 3) the free end of its blower damper 23 is swung up to engage the under face of the mounting plate; when so positioned the auxiliary damper 29 is rocked downwardly from the auxiliary opening 17 to open up communication therethrough. In its opposite position (see Fig. l), the auxiliary damper is swung up. parall'el with the mounting plate 26) and in engagement therewith, thereby to close the auxiliary opening 17; in this same position, the blower damper 28 is rocked downwardly and away from the inlet opening 15 to open up communication therethrough.

During operation of the burner it is expected that the motor blower unit M will also be in operation. The draft thereby created is discharged downwardly through the duct 14 to impinge upon the blower damper 28' which is thereby rocked downwardly to overcome the counterbalancing weight of the auxiliary damper 29. The blower damper is thereupon maintained in the normal open position of Fig. l. The air thus entering the duct in the base extension E is driven toward and into the drum D, some of it to pass through the inlet openings 6 and 7 of the pot burner B to support the fuel combustion therein. Should any current failure occur, operation of the motor-blower unit will stop, with a consequent cessation of the forced draft which is required for normal operation of the burner. In such circumstances, with no pressure of air impinging upon the blower damper 28, the overh'alan'ced duplex damper plate Wlll automatrcally rock itself to the position of Fig. 3 where. the auxiliary opening 17 is uncovered to admit air thereth'rough in a natural draft to travel toward and into the burner to support the combustion therein, although in a reduced volume. The special duplex damper means of this 1nvention, it will be noted, operates automatically whether the motor-blower be starting or stopping, to assure a continued air d'raft, either natural or forced, such as to maintain the burner in operation both safely and satisfactorily.

The auxiliary opening 17 is considerably larger in area than is the operating opening 15 that is in commnnication with the blower. This is advantageous because it admits a natural draft of air to the duct for travel to the burner in a fairly substantial volume, whenever there is failure of the blower to operate. In the auxiliary damper 29 there is a sufficient overbalance to be effective at all times except when a sufficiently greater draft force is exerted against the blower damper 28.

One feature of this invention is the pivotal mountmg of the duplex damper plate at a point that is relatively close to the duct top wall 10, yet with capacity to execute rocking movement of a sufficient range to provide ample area for the movement of air into the duct through either of the two inlet openings. This rocking movement need be through but 45 or so, as indicated in the drawing. The damper 29 at the auxiliary opening is arranged to swing from a full closing horizontal position downwardly to a point where it serves effectively as a deflector to change the direction of movement of the incoming air to the horizontal. This is advantageous inasmuch as it thereby tends to promote and assist the entering air in starting off in the right direction when first reaching the interior of the duct. it is also important that this damper effectively close off the auxiliary opening 17, when not in open position, so that air driven through the duct by operation of the blower will not escape uncontrolled into the atmosphere. It is of negligible importance, however, that the blower damper 28 fully close the operating opening 15, and its inability to do so (see Fig. 3) does not impair the natural draft of air passing through the auxiliary opening for movement through the duct. Because of these factors which are present, it is possible to offset the duplex damper plate transversely, and position one damper angularly with respect to the other, therebyto gain sufficient clearance for rocking movements which Will enable the damper plate to effectively open and close the two air inlet openings in the manner just" described;

The auxiliary damper 29- is desirably formed with a metering hole 32 of a size that is determined by the operating factors present. This hole communicates with the auxiliary opening 17 so that a restricted flow of air from within the duct to the atmosphere is always possible. When. the auxiliary damper is rocked to its closed position, the metering hole is disposed wholly to one side of the duct, i. e. adjacent its top wall 10 and just beyond. the dependin wall 25 and blower dam er 23 both of which act as a trifle to deflect the moving air stream downwardly and away from the hole. The air velocity within the duct is accordingly ineffective to force air out through the metering hole into the atmosphere. In the normal operation of the blower, air in a desired volume and pressure is circulated through the duct to enter the burner; if this volume of moving air be increased, the pressure will also increase, thereby forcing the air to seek an outlet wherever it may be. Themetering hole affords such an outlet which is effective under conditions of excess pressure to relieve some of the air within the duct. When no such excess pressure exists, there will be little or no outward movement of air through the metering hole.

in order that there may be a wide. margin of safety,

the auxiliary damper 29 should overbalance the damper 28 sufficiently to assure a wide clearance through the auxiliary opening 17 except when there is a substantial reduction in the air pressure directed against the blower damper 28-. This overb'alance need notbe great, as otherwise there would be no free and ready rocking movement of the duplex damper whenever the blower is in normal operation. it may be desirable, therefore, to em ploy a blower of such capacity as to deliver through the operating opening 15 air in a volume somewhat greater than that which is actually required for optimum performance of the burner. Under such conditions the duplex damper will, of course, be rocked normally so that the auxiliary opening 17 is closed, all except for the metering hole 32 within the auxiliary damper 29. With the duplex damper in this position, the air delivered from the blower is free to enter the duct E and advance therethroughto the burner. At the same time, if the air so moving through the duct be greater in volume than is desired, the excess will readily escape through the metering hole 32, as just described. This feature of the present duplex damper makes for safety and dependable operation.

, In Figs. 5---8 I have illustrated exactly the same du lex damper as'has heretofore been described, except that it is of rectangular contour and oppositely of a large opening in a vertical wall at one end or side of the duct E which leads to the furnace F. As best shown in Fig. 8, this opening is defined by an inturned flange 3'4 whereon is secured the marginal portion of a mounting plate 40 formed therethrough with air inlet operating and auxiliary openings 35 and 3'7, respectively. Upon this mounting plate is secured the motor-hlower unit base @2 which closely surrounds a discharge duct 44 leading from the blower housing 41 to the operating opening 35. Through this inlet and through the auxiliary opening 37 communication is assured with the interior of the air duct E which may constitute an extension of the drum base 5, the same as shown in Fig. l.

The auxiliary opening 37, as shown, is of rectangular contour with one of its long straight sides disposed proximate to the operating opening 35'; and extending laterally from the free edge of this straight side is a pair of spaced ears 46 which constitute supporting hooks. A duplex damper is provided with 'a transverse Wall St? connecting offset dampers 48 and 49 which are arranged to coact, in alternation, with the operating and auxiliary openings 35 and 37, respectively. At the line (,7 where the auxiliary damper 49 joins with the connecting wall 50 there is approximately a right angle but at the other line d where the connecting wall 56 joins with the blower damper 48 the angle is obtuse. Adjacent the juncture line a is a pair of aligned spaced slots 51 through each of which is extended one of the cars 46 which may be inclined slightly inwardly to provide a pivoted support for the duplex damper plate whose opposite ends are in counterbalancing relation. When operat ively assembled in place, the duplex damper plate is free to rock between two positions in one of which (see the'dotte'd line show ing in Fig. 8), the free end of the blower damper 48 is swung inwardly to engage the proximate face of the mounting plate 40; when so positioned, the auxiliary damper 49 is rocked outwardly away from the auxiliary opening 37 to open up communication therethrough. In the normal operating position, however, (see the full line showing in Fig. 8) the auxiliary damper 49 is swung inwardly into parallelism with the mounting plate and in engagement therewith, thereby to close the auxiliary opening 37; in this same position the blower damper 48 is rocked outwardly and away from the operating opening 35 to open up the maximum of communication therethrough.

The auxiliary damper 49 is provided with a metering hole 52 the same as already described in connection with Figs. 1-4, the purpose being to relieve air pressure from within the duct whenever the volume of air passing therethrough exceeds a predetermined amount. The counterbalancing action of the auxiliary damper is such that it normally rocks to open position whenever the blower operation stops, slows down, or falters. Under such conditions, air in a natural draft will enter through the auxiliary opening 37 to pass through the duct E to the burner (see Fig. 6). This abnormal position of the duplex damper will continue only so long as the blower is not performing; with resumption of operation a forced draft will again be created to move through the duct, and any excess of pressure therein will be relieved by escape of air through the metering hole 52 (see Fig. 6).

I claim:

1. A damper unit for use in an air supply duct having a blower inlet and a natural draft inlet comprising, a pivotally mounted duplex damper plate having a blower damper and an auxiliary damper for alternate closing of the blower inlet and natural draft inlet respectively, a connecting wall between said auxiliary and blower dampers for mounting said plate to the duct between said inlets, and means for pivotally connecting the connecting wall to the duct, said auxiliary damper extending from one side of and approximately normal to said connecting wall and said blower damper extending from the other side of the connecting wall and forming with the connecting wall an obtuse angle facing the blower inlet whereby the blower damper when closed will hold said auxiliary damper in an open air deflecting position.

2. A damper according to claim 1 wherein the means for pivotally connecting the connecting wall to the duct comprises means at the juncture between the blower damper and connecting wall defining a pair of slots and a pair of ears mounted on the duct and positioned in said slots.

3. A damper according to claim 2 wherein said auxiliary damper is provided with a metering hole for relief of air within the duct to the atmosphere.

References Cited in the file of this patent UNITED STATES' PATENTS Number Name Date 1,286,489 Anderson Dec. 3, 1918 1,945,223 laden m Jan. 30, 1934 2,005,852 Broderick June 25, 1935 2,147,801 Scanlan Feb. 21, 1939 2,251,055 Howard et a1 July 29, 1941 2,337,676 Mirra Dec. 28, 1943 2,351,878 Russel June 20, 1944 2,372,726 Langdon Apr. 3, 1945 FOREIGN PATENTS Number Country Date 428,633 Great Britain May 16, 1935 

